Garbage bags can be pretty handy components of an HVAC contractor’s tool kit, recent research at Lawrence Berkeley National Laboratory (LBNL) has confirmed (see “Air Flow Measurements in the Bag,”HE Sept/Oct ‘02 p. 8).Toting around a laundry basket is also a good idea. Indeed, contractors can often diagnose HVAC system pressures more accurately by using these common household objects than they can using commercially available flow hoods. Over the last couple of years, the Energy Performance of Buildings Group at LBNL has been investigating methods for improving the measurement of register air flows in homes, after earlier research had found serious precision problems when using commercially available flow hoods. Even the best ones had measurement errors of about 25% and some were much worse.We found that these devices typically had the following problems. Sensitivity to placement. Commercial flow hoods need to be centered to work properly.However, their large openings relative to the size of residential registers means that great care must be taken to ensure good centering. Since registers are normally sited near wall/floor,...